I have installed a Ubuntu 17.04 (64 bit) on my server.
Next I have installed the http Apache 2 (version 2.4) server and enabled subversion on it.
No special configuration is done :
In apache2.conf, added the following :

I have separated the site-available in two separate sites.
One for www and another for subversion....for some reason this solves the issue ???
Now I can access the subversion site, from an external IP, and download with real speed (3 Mb instead of 20 kb).
Also the two site are splitte in two different domains (www.mydomain.com and svn.mydomain.com)